The present disclosure relates to a fixing device and an image forming apparatus.
An electrophotographic image forming apparatus includes a fixing device that fixes toner on a recording medium. The fixing device fixes toner by applying heat and pressure onto the recording medium while the recording medium carrying unfixed toner is passing through a pressure nip formed between a heating rotatory body and a pressure roller. A heater that heats the pressure nip is provided inside of the heating rotatory body.
While the heater is heating the heating rotatory body, the heating rotatory body or the pressure roller is thermally-expanded. Such thermal expansion may cause fluctuation of the conveyance speed of the recording medium at the pressure nip, leading to blurring in an image that is formed. The heating rotatory body may be deformed if heated while in a suspended state. Some fixing devices employ an optical sensor (a reflective sensor or a transmissive sensor) to detect the rotation state of a heating rotatory body and control the heating rotatory body to maintain an appropriate rotation speed. Generally, a semiconductor device is used for such an optical sensor.